The National Crime Agency investigation into Arron Banks will inevitably examine his contacts with Russian officials in the run-up to the EU referendum, and a series of apparent deals offered to him by Moscow.

Banks also rejects the commission’s suspicion that he is not the “true source” of £8m funding supplied to Leave.EU.

Arron Banks faces criminal inquiry over Brexit campaign

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But the businessman has given shifting and evasive explanations for his multiple meetings with Russian diplomats and suspected spies, which began in autumn 2015. He initially said he had met once with Russia’s ambassador in London, Alexander Yakovenko.

Banks subsequently conceded that three meetings had taken place. He later revised the figure up to four in an interview with the New York Times. The evidence indicates that the Russian embassy ran a major operation to cultivate and support Banks in the crucial months leading up to the vote.

The question the NCA will want to answer is whether Kremlin money may have found its way to Leave.EU and Banks. In a statement, Damian Collins, the chair of parliament’s digital, culture, media and sport committee, said it was unclear from where Banks had got the cash.

“He failed to satisfy us that his own donations had, in fact, come from sources within the UK,” Collins said on Thursday.

Collins noted the potential gold and diamond deals the Russians offered to Banks. This year the Observer revealed that in October 2015 Alexander Udod, a Russian diplomat, invited Banks and his business partner Andy Wigmore to meet Yakovenko.

Udod was later expelled from the UK as a suspected spy, in the wake of the novichok poisoning of Sergei and Yulia Skripal. On 6 November 2015, Banks and the ambassador had lunch. Eleven days later Yakovenko introduced Banks to Moscow businessman Siman Povarenkin.

Using a PowerPoint presentation, Povarenkin invited Banks to pump money into a lucrative scheme to consolidate Russia’s gold industry. The pitch said the deal was backed by powerful Kremlin entities, including the state bank Sberbank. That meant “opportunities not available to others”.

Banks says he decided not to take advantage of the private Russian offer, made during the week of Leave.EU’s official launch. He says that he is the victim of a smear campaign by hostile pro-remain journalists.

However, Banks was sufficiently interested in Russian gold to pass the presentation on to fellow leave campaigner Jim Mellon. In January 2016, Banks also corresponded with Udod, the alleged spy.

The embassy and Povarenkin subsequently offered Banks another opportunity to invest, this time in the state-owned Russian diamond company Alrosa. In May 2016 Banks met with another Russian, Ilya Karas, to discuss a possible investment in another goldmine in Guinea, in west Africa. Banks says he declined both offers.

The Russian embassy says there is nothing sinister about meeting stakeholders and points out that dealing with people from across the political spectrum is part of the job. It denies interfering in the referendum.

And yet the extensive and sustained nature of Yakovenko’s interactions with Banks suggest that – at minimum – the Russians viewed him as a useful source of intelligence.

In the year of the Brexit referendum, Banks, Wigmore and Nigel Farage travelled regularly to the US to support Donald Trump’s presidential campaign. Banks and Wigmore met Yakovenko in August 2016.

There is evidence to suggest that Moscow sought to influence the outcome of the two most consequential votes of modern times: the election of Trump and Brexit.